The present disclosure relates to an image reading apparatus for scanning documents, an image forming device, and a method for controlling an image reading apparatus.
An image reading apparatus scans a document and generates image data. In some cases, an image reading apparatus is provided to an image formation device, such as a multifunctional peripheral, copier, fax machine, or the like. Noise arises during document scanning operations. Moreover, in cases in which a copy job or the like [is executed] by an image forming device, when document scanning and printing are performed in parallel, considerable noise is generated. In most cases, image reading apparatuses and image forming devices are situated in workplaces, such as companies and government offices. For this reason, it is preferable for [such devices] to generate less noise. Thus, in some cases, image forming devices are equipped with a mode for suppressing the sound arising during printing operations.
Image forming devices such as the following are known [in the prior art]. Specifically, one known image forming device optically scans documents, and accepts selection of a normal mode or a reduced-noise operation mode; and when the reduced-noise operation mode has been selected, in cases in which both a document scanning operation and a printing operation are to be executed, controls the interval of overlapping operation of the auto-scan operation, during which a document is scanned by the scanning section while being fed by the document auto-conveying device, and the printing operation by the print engine section, such that this interval is shorter than when normal mode has been selected. Through this configuration, operating noise generated in cases in which both a document scanning operation and a printing operation are performed [simultaneously] is suppressed.
In image reading apparatuses, there are cases in which a stepper motor is employed for document conveying, for move of the light source section, and so on. A stepper motor rotates through input of a pulse signal. Vibration arises based on rotation of the stepper motor.
The magnitude of the vibration arising based on rotation of a stepper motor varies in accordance with the frequency of the pulse signal. In particular, the closer the frequency is to one at which characteristic vibration arises, the greater is the vibration that arises on the basis of rotation of the stepper motor. As a result, depending on the frequency of the pulse signal, there may be cases in which noise due to vibration (sometimes termed “chattering noise”) arises.
In image reading apparatuses, it is necessary to input to the stepper motor a pulse signal of a frequency that will not result in high levels of noise due to vibration. However, the frequency of the pulse signal such that characteristic vibration would arise (such that the stepper motor or the like vibrates through resonance) will vary according to factors such as the shape of the stepper motor case, the method of attachment of the stepper motor to the frame, and the like.
The rotation speed of a stepper motor is determined on the basis of the rotation speed required to meet specifications. For this reason, in some cases, the frequency of the pulse signal is not set in a manner that takes noise caused by vibration into consideration. While selection of the frequency of the pulse signal and of the stepper motor is performed during the initial design stage with a view to suppressing noise caused by vibration, modifications to the rotation speed of the stepper motor necessitated by the need to improve the scanning speed, modifications to the shape of the case, or modifications to the method of attachment of the stepper motor due to improvements or design modifications, may in some cases lead ex post facto to considerable vibration on the basis of rotation of the stepper motor, and to noise based on vibration.
Additionally, in an image reading apparatus, the move speed of the document and of the light source section is varied to match the enlargement factor during scanning of a document. The greater the enlargement factor for scanning the document is, the slower the move speed of the document and of the light source section will be, and the narrower will be the width per line in the sub-scanning direction. Stated another way, the greater the enlargement factor is, the greater the scanning resolution in the scan will be. For example, when the enlargement factor is 200%, the move speed of the document and the light source section is one-half that when the enlargement factor is 100%. Such a scanning system is in some cases referred to as an “optical zoom system.”
When the move speed of the document and the light source section is varied to match the enlargement factor during scanning of a document, the rotation speed of the stepper motor also changes in accordance with the enlargement factor. Therefore, depending on the enlargement factor, there are cases in which the frequency of the pulse signal may be a frequency that leads to considerable vibration on the basis of rotation of the stepper motor, and to noise based on vibration. Stated another way, depending on the enlargement factor, there are cases in which a pulse signal of a frequency such that chattering vibration will arise is input to the stepper motor. In this way, there exist certain enlargement factors, at which the noise arising during operation of the image reading apparatus becomes considerable.
In the past, expensive stepper motors of low-vibration type were adopted in some cases, in order to suppress the level of vibration on the basis of rotation of the stepper motor, and noise based on such vibration. In some cases, other measures, such as providing additional vibration-damping members such as rubber, or sheets that convert vibration to heat, were adopted. For this reason, a problem encountered in the past was that, in some cases, suppression of vibration and of noise arising due to vibration led to a higher manufacturing cost of the image reading apparatus.
The prior art techniques discussed above merely involve setting to zero, or shortening to the greatest extent possible, the duration of overlap between the scanning operation and the printing operation, so as to suppress noise generated by an image forming device. Consequently, such techniques cannot solve the problem of cases of high levels of vibration arising during scanning of a document, and of noise generated by vibration, encountered when stepper motors are employed.